SPC Feb 24, 2018 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0609 AM CST Sat Feb 24 2018
Valid 241300Z - 251200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
NORTHEAST TEXAS...NORTHWEST LOUISIANA...ARKANSAS...SOUTHEAST
MISSOURI...SOUTHERN ILLINOIS...FAR SOUTHWEST INDIANA...WESTERN
KENTUCKY...WESTERN TENNESSEE...FAR NORTHWEST ALABAMA...NORTHERN
MISSISSIPPI...AND NORTHERN LOUISIANA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK,AND EXTENDING WEST INTO NORTH TEXAS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED AND SLIGHT RISK AREAS...
...SUMMARY...
Severe thunderstorms are expected to develop today through tonight
across northeast Texas and the Arklatex region, east northeastward
through the lower Mississippi and lower/middle Ohio Valleys. The
storms will be accompanied by potential for damaging wind gusts and
a few tornadoes, a couple of which could be strong. Hail will also
be possible across the Texas and Arklatex portions of the outlook.
...Synopsis...
Large-scale troughing will persist over the western and central U.S.
this period, while ridging holds fast across parts of the Southeast
and adjacent western Atlantic. At smaller scales, an energetic
short-wave trough -- embedded within the larger-scale cyclonic flow
-- is crossing the central and southern Rockies, and will progress
east-northeast across the Plains, reaching the upper Great Lakes by
the end of the period.
At the surface, a rather weak/ill-defined pattern is evident at this
time, per latest surface analysis, with a very weak low over far
northeast Oklahoma, a warm front extending roughly eastward to
Kentucky, and a cold front extending southwest across eastern
Oklahoma and north central Texas into the Concho Valley and Big Bend
area. With time, as the upper system shifts east-northeast, the
northeast Oklahoma low is progged to gradually deepen/shift slowly
north-northeast across Missouri today, and then advance more rapidly
north across Illinois into the western Upper Great Lakes region
overnight. As this occurs, a strengthening cold front will move
eastward in the wake of the low, extending across Arkansas and
eastern Texas by sunset, and then accelerating east to reach a
position just to the lee of the Appalachians by the end of the
period (early Saturday morning). This front will focus a zone of
strong/severe storms through the period.
...Portions of North Texas east across the lower Mississippi and
Tennessee Valleys, and northeast to the Mid-Ohio Valley...
Elevated Convection has begun to develop across the eastern
two-thirds of Texas this morning, as large-scale ascent increases
atop a still-stable boundary layer as the southern Rockies upper
system advances. With steep lapse rates over the area supporting
moderate CAPE and strengthening mid-level flow, a few of these
storms will pose a risk for producing large hail.
Several complicating factors with respect the evolving severe risk
-- primarily centered around the developing Texas convection and
more widespread storms which have been ongoing from the Ozarks east
across the Ohio Valley states. Resulting cloud cover and
reinforcement of cool air to the north of the warm front will affect
potential for any later-day heating/destabilization, and so later
adjustments to the outlook may be needed as the environment evolves.
With that said, very strong/veering wind profiles with height --
already indicated particularly over western portions of the region
-- will continue to strengthen, as stronger flow aloft associated
with the advancing upper trough overspreads the outlook area. By
afternoon, very large, sickle-shaped low-level hodographs --
representative of low-level shear highly favorable for updraft
rotation -- can be expected, suggestive of tornado potential with
any sustained/stronger storms. However, as implied above,
thermodynamic concerns will temper overall risk to some degree.
At this time, expectations are that ongoing Texas convection to
spread northeastward across eastern Oklahoma/Arkansas with time,
with new storm development late this morning/afternoon occurring
across northeast Texas/southeast Oklahoma/the Arklatex region.
While storm mode should trend toward a linear configuration near the
front, supercells -- perhaps just ahead of the line but particularly
within what is likely to be a complex line with LEWPs and bows --
are expected to evolve. Along with risk for fairly widespread
damaging winds, a few tornadoes will be possible. Greatest tornado
risk -- including potential for a couple of strong tornadoes -- is
expected within a corridor from the Arklatex area northeast across
Arkansas into the southeast Missouri/southern Illinois/western
Kentucky/western Tennessee area this afternoon and evening.
Greatest wind risk will exist along a similar corridor.
Overnight, as convection spreads east across the Mississippi Valley,
storms will eventually begin to diminish in intensity -- due both to
a decrease in instability, as well as low-level flow becoming
aligned more parallel to the front as the upper system shifts
northeast toward the Upper Great Lakes region, away from risk area.
Until then however, risk for a tornado or two within the complex
convective line along with damaging wind risk can be expected into
the western Kentucky/western and Middle Tennessee/northwest
Alabama/northern Mississippi/northern Louisiana areas.
..Goss/Marsh.. 02/24/2018
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